Validity and reliability of the Cataract TyPE Spec: an instrument for measuring outcomes of cataract extraction.

Purpose: To design and validate a survey instrument that measures vision-related functional status, which is appropriate for self-administration in a clinical practice and mail survey setting.

Design: Observational, validation study in sequential patients.

Methods: A prototype visual function instrument (the Cataract TyPE Spec) was developed based on focus group input and then validated in an outcomes study conducted among 1,823 patients who underwent cataract extraction performed by 22 surgeons at six centers in the United States. Reliability was determined by calculating Cronbach alpha for different types of administration (self-administration at the site of care and mailed survey) and across race and gender. Criterion validity was determined by correlating scores on the TyPE Spec with baseline measures and changes in visual acuity, overall rating of vision, and general quality of life.

Results: The instrument was internally valid (Chronbach alpha = 0.94), both on self-administration in the patient care setting and upon mailed survey administration and across patient race and gender. The TyPE Spec score was highly correlated with overall rating of vision (r =.54, P <.0001) and moderately correlated with Snellen acuity (r =.32, P <.0001), rating of vision in the better eye (r =.42, P <.0001), and quality of life, as measured by the physical component summary score of the SF-36 (r =.27, P <.001). Change in TyPE Spec similarly correlated with change in rating of vision overall, change in best-corrected Snellen acuity, and change in rating of vision in the operated eye.

Conclusions: The cataract TyPE Spec instrument was found to be equally valid and internally consistent when administered in the patient care setting and by mail survey.